class CppState: # export

    def __init__(self):
        self.__pair_square = ['[', ']']
        self.__pair_curly = ['{', '}']
        self.__pair_ext = ['<', '>']
        self.__pair_paren = ['(', ')']
        self.__pair_c_comment = ['/*', '*/']
        self.__pair_special = ['?', '?']
        self.reset()

    def reset(self):
        self.curly = 0
        self.square = 0
        self.ext = 0
        self.paren = 0
        self.in_c_comment = False
        self.in_cpp_comment = False
        self.in_special = False
        self.rule = []
        self.rules = []
        self.things = []

    def optional(self):
        return self.square != 0 or self.curly != 0

    def update(self, tok, line):
        if not self.in_comment():
            if tok == '[':
                self.square += 1
                self.things.append(self.__pair_square)
            elif tok == ']':
                self.square -= 1
                assert(self.things.pop() == self.__pair_square)
            elif tok == '{':
                self.curly += 1
                self.things.append(self.__pair_curly)
            elif tok == '}':
                self.curly -= 1
                assert(self.things.pop() == self.__pair_curly)
            elif tok == '(':
                self.paren += 1
                self.things.append(self.__pair_paren)
            elif tok == ')':
                self.paren -= 1
                assert(self.things.pop() == self.__pair_paren)
            elif tok == '<':
                self.ext += 1
                self.things.append(self.__pair_ext)
            elif tok == '>':
                self.ext -= 1
                assert(self.things.pop() == self.__pair_ext)
            elif tok == '?':
                if not self.in_special:
                    self.in_special = True
                    self.things.append(self.__pair_special)
                else:
                    self.in_special = False
                    assert(self.things.pop() == self.__pair_special)
            elif tok == '/*':
                self.in_c_comment = True
                self.things.append(self.__pair_c_comment)
            elif tok == '*/':
                raise Exception("Unmatched closing C-style comment mark", tok, "in line", line)
        else:
            if self.in_cpp_comment:
                if tok == '\n':
                    self.in_cpp_comment = False
                    return
            if tok == '/*':
                raise Exception("Nested C-style comment", tok, "in line", line)
            elif tok == '*/':
                assert(self.things.pop() == self.__pair_c_comment)
                self.in_c_comment = False

        if self.curly < 0 or self.square < 0 or self.ext < 0 or self.paren < 0:
            raise Exception("Unbalanced BNF bracket", tok, "in line", line)
        return self.optional()

    def in_list(self):
        return self.curly > 0

    def in_option(self):
        return self.square > 0

    def in_paren(self):
        return self.paren > 0

    def in_ext(self):
        return self.ext > 0

    def in_comment(self):
        return self.in_c_comment or self.in_cpp_comment

    def in_something(self):
        if len(self.things) == 0:
            return None
        return self.things[-1]

    def is_optional(self):
        return self.in_list() or self.in_option()